In a conventional class D amplification device, an output PWM signal, which is an output signal obtained by switching (on/off) a constant voltage obtained from a DC power supply, is input to a low-pass filter (LPF), and demodulated to an analog audio signal to reproduce sound.
In high-speed switching elements (MOS field effect transistors) of a highside disposed on a higher potential power supply side and a lowside disposed on a lower potential power supply (or ground) side in a half bridge circuit, a delay occurs in rising and falling of the switching due to input capacitance characteristics or variation of an element. For that reason, in order to reduce a through-current caused by turning on the paired switching elements at the same time, a dead time is intentionally provided so as to turn off both of those switching elements at the rising and falling times of a switching element driving PWM signal which is input to gates of the switching elements of the highside and the lowside.
If the dead time is increased for suppressing heat generation, a dead zone in which an output voltage is not detected as an input signal occurs in the vicinity of a low output voltage. As a result, an audio output amplitude is decreased and distorted to largely affect a sound quality. That is, the heat generation generated by the through-current and the deterioration of the sound quality due to distortion generated by the dead time have a relationship of tradeoff.
As the conventional class D amplification device, there has been known a digital switching amplifier in which, in order to flexibly control the dead time so as to suppress a through-current flowing in a bridge circuit at the time of reproducing a large volume of sound while suppressing the distortion of a reproduced signal at the time of reproducing a small volume of sound, a dead time controller controls, in cooperation with a volume controller, the dead time to be decreased when the small volume of sound is reproduced by the volume controller, and to be increased when the large volume of sound is reproduced (for example, refer to Patent Document 1).